1. Technical Field
The present invention relates generally to switching in a packet switched network and, more specifically, to systems and methods for translating network addresses within a network device.
2. Background Art
At the heart of most networks are switches interconnected via a communications medium. For example, Ethernet is a commonly used local area network scheme in which multiple stations are connected to a single shared serial data path. These stations communicate with a switch located between the shared data path and the stations connected to that path. The switch controls the communication of data packets on the network.
Networks are frequently organized into sub-networks, called subnets. Within a single subnet, packets of information may be directed to their destination devices using a layer 2 Media Access Control (MAC) address that identifies the attached Ethernet devices. When a switch receives a packet with a familiar destination MAC address, it forwards the packet to the output port associated with the MAC address.
Packets being transmitted between layer 2 subnets travel through the network using the destination device's IP (Internet Protocol) layer 3 address. More particularly, a transmitting device sending a packet to a destination device outside of the transmitting device's subnet first determines, using the IP layer 3 address, the layer 2 MAC address of a gateway router that bridges the subnets. The gateway router, upon receiving the packet, performs address translation, which involves stripping the MAC destination address of the router and inserting a new MAC destination address that corresponds to the MAC address of the destination device in the destination subnet. The router determines the MAC address to substitute based on the IP address.
Generating and substituting the new MAC destination address for the old MAC address incurs additional overhead for the gateway router that is not experienced by the layer 2 switches. Accordingly, the gateway router may require more time to transmit its received packets than the layer 2 switches. This can be problematic for certain applications, such as multimedia applications, that stream large numbers of packets across subnets. Ideally, it is desirable to reduce routing latency to match switching latency so that delay-sensative traffic can stream across subnets without disruption.
Thus, there is a need in the art to improve layer 3 routers to reduce latency during MAC address translation.